Microwave test equipment



0d 6 1953 H. J. RIBLET MICRowAvETEsT EQUIPMENT 2 Sheets-Sheet 1 Filed Dec. l, 1949 gml Imm ATTO/@V67 Oct. 6, 1953 H. J. RIBLET 2,654,863

MICROWAVE TEST EQUIPMENT Filed nec. 1. 1949 2 sheets-sheet 2 Paieniea Oct. e, 1953 2,654,863

UNITED STATES PATENT OFFICE MICROWAVE TEST EQUIPMENT Henry J. Riblet, Belmont, Mass., assignor. to Raytheon Manufacturing Company, Newton, Mass., a. corporation of Delaware Application December 1, 1949, Serial No. 130,422

3 claims. (o1. S24- 58) l 2 This invention relates to equipment for deter- In order to automatically divide the energy of mining the standing Wave ratio in Wave guide one slot by the energy of the other slot, applistructures, and more particularly for determincant modulates the energy source, providing, for

ing the degree of mismatch between a load and example, energy pulses having a repetition rate a wave guide as Well as the phase of the load im- 5 of 1G00 pulses per econd. Detection of the enpedance over a wide range of frequencies. orgy picked up by the slots then produces non- Tlie conventional Way of measuring the standsinusoidal one kilocycle signals. These are ing Wave ratio in Wave guide structures utilizes passed through iilters, the output of one slot a longitudinal slot in the wave guide through 1 being passed through a filter which passes one which a probe pickup may be inserted into the O kilocycle and the output of the other slot being Wave guide. Movement of the probe along the passed through a filter which passes three kiloslot causes alternate maximum and minimum cycles. rhe outputs oi these filters are fed to a voltage magnitudes to be induced in the probe, Common amplifier, and the resultant amplified and from these the standing- Wave ratio may be Signals are again separated by filters. The outcomputed. Also, the phase of the load impedput one of the operating iilters is used to conance may be computed where the distance in trol the bias of the common amplifier similar electrical wave lengths from the load to the probe to the automatic volume control of conventional can be measured. radio receivers, thereby causing a decrease in The present invention comprises a system y the amplification of the other signal in propor- Whereby the standing Wave ratio and the phase 'M' tion to the amplitude of the iirst signal. The

of the load impedance may be continuously and other signal 110W has an amplitude WhCh C01"- automatically measured, computed and displayed responds to the quotient oi" the two signals, and over a Wide range of frequencies. In addition, the measurement 0f the magnitude of this signal at need for mechanical movement of a probe in the Successive maxima and minima will give a true wave guide is eliminated. This is accomplished J indication of the magnitude of the standing wave by the use of a pickup device Connected te the ratio. This invention further provides for con- Wave guide which is insensitive to variations of tinuous display of this quotient by feeding the frequency. The frequency of the source is varied quotient signal to the vertical deflection plates by a certain predetermined amount, thereby 0i a cathode ray tube. The horizontal deflection causing a change in the number of electrical te plates are connected to a source of voltage which Wave lengths between the load and the pickup. Varies prOlOOlODeey With the 'refiueny 0f the This Causes the pickup, in effect, 1-,0 move through microwave source, with a result that the maxima a plurality of voltage maxima and minima proand minima are displayed 0n the Cathode ray duced by the standing wave, which results from tube screen to form a picture similar to that of e eomnnetien ef energy being fed te the leed 35 the modulation envelope of a conventional amand energy being fefleeted from the 10a@ plitude modulated communication signal.

For a freqneneynnsenstve voltage pickup, Further advantages of this invention Will be the invention may utilize a Wave sampler comeplelent as the description thereof progresses, prising a pair of slots, one in each of the Wider reference being had to the accompanying drawsides of the main Wave guide. The centers of i0 ings wherein: these slots both lie in a plane which is perpendic- Fig. l illustrates a functional block diagram of eier to the (innemen ef propagation of the energy an electrical system utilizing. the present invenin the guide. In addition, the major axes of tion; these slots are at right angles to each other with Fis. 2 illustrates a longitudinal Cross-sectional the result that the instantaneous energy picked VeW 0f the Wave Sampler Sher/r1 in Fg- 1 taken up by the slots differs from each other by a phase along lille 'f- -J Fig. 3 and of substantially 90 electrical degrees. These slots Fig. 3 illustrates a transverse cross-sectional are each coupled to a separate wave guide and View 0f the device Shown in Fig. 2 taken along behave in the saine manner as probes in the line 3 3 of Figi Wave guide which are separated from each other 50 Referring 110W t0 Fg- 1, there is shown a miby a quarter wave length at all frequencies. The CIOWai/e generator i which is tunable over a relquotient of the amplitudes of the energy fed tively Wide range, fOr eXmple, ten per cent, of through these slots is an accurate measure of its frequency. This microwave generator may the standing wave ratio at the maxima and be, for example, a conventional magnetron or minima. 55 klystron which is mechanically tuned in a Wellknown manner. The output of microwave generator I which, as is shown here by way of example, is pulsed at the rate of 1000 pulses Iper second, is fed to a wave sampler 2 through any desired wave energy transfer means 3 such as, for example, a Wave guide.

Microwave energy is fed from energy transfer means 3; through wave sampler: Z' to a load. 4 through energy transfer means 5, for example, a waveguide. The load 4 may be of any desired impedance whose magnitude and phaseY are to be measured. It may be, for. example, a rotating joint which is being tested to determine its mismatch to energy transfenmeansi 5?. over a range of frequencies;V The-loutputoff the wave sampler is fed into two channels 6 and" 'I, respectively. Y*

Referring now to Figs. 2 and'3, there is shown a wave sampler particularly adapted.' use:

with wave guide structures. The wave sampler comprises a, main wave guide; 2-.-'I, one enel of which connects; to.: genera-tor I-. through. energy transfer means; 3.-, andv the other: end. of,v which connects to loadV 4f` throughv energy transfer means Guide 2'1, which; is.- rectangular., has ai longitudinal slot 2.85m'. the; lower sidey thereof adjacent-one of the` sideA walls,A and a transverse slot 2.9; in; the upper; side thereof. The centers off slots; 2.8 andi` 29 lie inraplane which isper.- pen-dicular to; the` direction` of. propagation: of energy. iiiguideV 211;

Slots 28; and 29.- couple-i energy from guide v2.1 into auxiliary guides. 30, and 3-I, respectively. One. end of guidellzis; connected tochannel 6 and-the' other end thereof terminates in energy absorbent. material 32. Similarly, one. endi of guide 3l is. connectedi to .channel 'If and-the.- other end-thereofv terminates in energy absorbent mater-.iaiv 33.

Sincey slot 2.9 is energized: byy electrostatic fields, while slot 28- is energized by electromagnetic iields, the energy propagated: in guide 30 differs. fronrl the energy propagated in` guide 3.I- by substantially ninety electricaldegrees. The construction and: operation of this'. wave sam- Dler are describedin'. greater. detail incopending application of TheodoreS. Saadi,..Ser-ial.No: 30;(l41, filedt May- 29,. 1948, now Patent; No 2,636,082-,- dated. April. 2l, 1953i Channelsr 6 andx 'I-v feed. microwave detectors and 9,-.respectively which. mayv be ofany desired type,y such= ascrystals,Y barrettersv or thy-- rite elements.. The outputsl of; the detectors whichY producea,v signal of the,- frequency` of. the pulses of themicrowave f source are nonsinusoidal andconform substantially to the-modulationl envelope of the microwavei signal.Y rllhe output ofV detector 8fis.` fed. through. a sharplytuned lter. amplifier I which passes onekilocycle signals, while the output of detector l) is fed to asharply-tuned lter. amplifierLv I I- which basses. three kilocycle; signals.V Theoutputs of filter amplifiers I0 and II are fed to a common mixer amplifier I2. The. outputfof. mixer. amplier I2` isfed toathreekilocycle filter-amplifier I3 which passes threekilocycle signals. and to, aone. kilocycle amplifier, I4T which; passes 1 one kilocycle. signals... The .output-ofthe.. three. kilo:-

cycle lter amplifier I3 feeds;a.. detector 26; whichin, turn; feeds a direotzcurrent amplifier I5.. The output of amplifier I;I is.used tacontrolf. the gain, ofthe;- mixerampliiier l2; forexample, bybeingapplied; to: the bias; control of variablezmu.tubesinamplier |21. The detectori is .of such'a polarity that theaoutputzoffam plier I5 reduces the gain of amplifier I2 as the magnitude of the three kilocycle signal increases. The result is that the output of filter amplifier I4 varies as the ratio of the amplitude of the signal in channel 6 to the amplitude of the signal in channel 1.

This voltage ratio computer is disclosed by way ci' example.A only anyr mechanical or electrical computer which would perform the desired function could be used.

The output of lter amplifier I4 is fed toa vertical deflection plate I6 of a cathode ray tube IT, the opposite vertical deflection plate I8;f..being:gioundextL One of the horizontal deectionaplates.I29iisgrounded and the other horizot-ital'deflection` plate 20 is connected to the movable arm i2.I of. a potentiometer 22, whose ends are connected" across a battery 23, a center platee: 24 of which is grounded. Movable arm 2I is mechanically ganged? to the tuning arrangement;v of 'microwavegenerator Ig, said, arm. and tuningr arrangement having,- simultaneousr metion'. impartedtheretu-fby any desired means, such; asi motor-` 25;.

Energization of motor. 2.5 causes potentiometer arm: 2t totmovefromcnesend of potentiometer- 22;v to-thesothen thereby causing. the.v trace. of the.v cathodee raytube-- IT, to.- move horizontally acrossthescreen.. Simultaneously microwave genera/ton I- tuned, causing, successive maxima and mnima', of the standing?. wave in energy transfer means 5: to bia-.pickedV up by wave. samfplea:I 2.- These` maxima., and minima arel fed4v through. theV voltage.. ratio computer and applied tot-ther verticaldeectioniplatesf of the. cathode ray.- tube causing displacementfof` the trace vertically.- in proportion. tol the; magnitude of the maxima and minima. These maximaand. mini,- maf.. may. be measured. directlyA on. the. cathode ray tubescreen, or. thepresentation. on fthe. screen may be photographed and, measurement Vmade fnomr the. photograph. The number,r of maxima and minima which will appear across the screen of@ the cathode-fray tube willbe. proportionalv` to the;` number. of` electrical. wavelengths separat.- ingwave sampler 2, and lcad.4..andl tothe magg` nitude: of-A the. frequency change of microwave generator. I.m

Eer. example if wave sampler 2. is, separated from-z loadI 4 byaT wave: guide. of 1,00 electrical wave. lengthsat. a. given.; frequency of.V microwave generator. I.andithe.frequency o fmicrowave generatou Iris:4 increasectby` ten.. per. cent,4 the..num, her of; electrical @wave wave lengths. between. wave samplerv- 2.- andr theload.l 4; will be increased by ten per cent ouby` ten wavelengths. Since there aratwo maxima andztwo .minima in. eachwave length, 2.0v maxim-a and 210.- minima will` have passed.y throughL wave sampler. 2f during. the' ten per centirincrease inthe frequency. .ofvv microwave generator. I ThesemaximaJ and minima are.. fed throughA theF detector lter and. ratior computer systems and-.willlbe displayedon thev screen of cathoderay-tuba lh. By measuringfthe. ampli-- tude;differences-betweenV successivemaxima andv brated by substituting a short circuit for1oad4; Y

and ascertaining the position of the maxima and minima on the cathode ray tube, this position corresponding to an impedance phase of plus 90 degrees. The phase of the load impedance may then be ascertained by linear interpolation between successive maxima and minima.

Equipment built in accordance with this invention enabled measurement of load impedance phase with an accuracy of plus or minus four degrees and a standing wave ratio with an accuracy of plus or minus eight per cent over a twelve per cent frequency range centered in the three-centimeter band.

This completes the description of the embodiment of the invention illustrated herein. However, many modifications thereof will be apparent to persons skilled in the art. For example, the microwave generator may be electronically tuned 4and the horizontal sweep for cathode ray tube I'i may be electronically generated, and, indeed, any desired indicating means, for example a meter, may be used instead of cathode ray tube I1. Also, the microwave generator may be sinusoidally modulated rather than pulse modulated and, indeed, the device may be used with a computer which does not require a common amplier i2, in which case the microwave generator need not be modulated. Therefore, applicant does not wish to be limited to the specic details of the embodiment of the invention illustrated herein except as dened by the appended claims.

What is claimed is:

1. An electromagnetic device comprising a source of electromagnetic energy, means for transferring energy from said source to a load, means connected to said transferring means for measuring the magnitude of said energy in said transferring means at a pair of discrete points, means responsive to said measuring means for computing the quotient of the amplitude of the energy at one of said points with respect to the amplitude of the energy at the other of said points, means for varying the number of electrical Wave lengths of said energy between said load and said measuring means, and means responsive to said computing means and said means for varying the number or electrical wave lengths for continuously displaying the relation between said quotient and said number of electrical wave lengths.

2. An electromagnetic device comprising a source of electromagnetic energy, means for transferring energy from said source to a load,

means connected to said transferring means for measuring the magnitude of said energy in said transferring means at a pair of discrete points, means for varying the number of electrical wave lengths of said energy between said load and said measuring means comprising means for varying the frequency of said source, means responsive to said measuring means for computing the quotient of the amplitude of the energy at one of said points with respect to the amplitude of the energy at the other of said points, and means responsive to said computing means and said means for varying the number of electrical Wave lengths for continuously displaying the relation between said quotient and the frequency of said energy.

3. An electromagnetic device comprising a source of electromagnetic energy, means for transferring energy from said source to a load, means connected to said transferring means for measuring the magnitude of said energy in said transferring means at a pair of discrete points, means for varying the number of electrical wave lengths of said energy between said load and said measuring means comprising means for cyclically varying the frequency of said source, means responsive to said measuring means for computing the quotient of the amplitude of the energy at one of said points with respect to the amplitude of the energy at the other of said points, and means comprising a cathode ray tube responsive to said computing means for continuously displaying the relation between said quotient and the requency of said energy.

HENRY J. RIELET.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,442,606 Korman June 1, 1940 2,454,042 Dettinger Nov. 16, 1948 2,456,800 Taylor et al. Dec. 21, 1948 2,479,650 Tiley Aug. 23, 1949 2,482,173 Hagstrum Sept. 20, 1949 2,562,281 Mumford July 3l, 1951 2,573,402 Chapman Oct. 30, 1951 2,580,678 Hansen et al. Jan. 1, 1952 2,605,323 Samuel July 29, 1952 OTHER REFERENCES Proceedings of the I. R. E, vol. 36, No. 12, Dec. 12, 1948, pages 1493 to 1499, presented, 1948 I. R. E. National Convention, March 24, 1948, New York, New York. 

